Share-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 717	$ 1,999
Income tax benefit	(181)	(744)
Share-based compensation, net of income tax benefit	536	1,255
Performance unit incentive plan (“PUP”)
Summary of share-based compensation expense
Share-based compensation before income tax benefit	194	1,316
Restricted stock
Summary of share-based compensation expense
Share-based compensation before income tax benefit	503	623
Restricted stock units
Summary of share-based compensation expense
Share-based compensation before income tax benefit	$ 20	$ 60